Growth dynamics of the small-bodied notosuchian Yacarerani boliviensis Novas et al., 2009 (Crocodyliformes; Notosuchia; Sphagesauridae) inferred from long bone histology

Abstract

Sphagesaurids are a group of notosuchians crocodyliforms that lived during the Late Cretaceous of Gondwana in South America. Although, Sphagesauria has previously been the subject of histological studies, there is a scarcity of information about some taxa within the clade, particularly within Sphagesauridae. The present study is focused on the long bone histology of Yacarerani boliviensis, a small bodied sphagesaurid notosuchian from the Upper Cretaceous of Bolivia. Our main goals were to obtain data regarding the ontogenetic stages of the studied individuals, the life history and growth dynamics of Y. boliviensis. We analysed thin sections from one humerus, one coracoid, and three femora from a monospecific assemblage. All elements are formed by zones characterised by woven bone and highly vascularised parallel fibered bone, with simple, longitudinal and reticular, vascular canals. The annuli are composed of avascular parallel fibered bone accompanied by a line of arrested growth (LAG). The analysed specimens do not exhibit evidence for somatic or sexual maturation, which is consistent with the open nature of the neurocentral suture of their vertebrae. The type of bone matrix suggests fast growth dynamics with periods of decline and even cessation of growth similar to that observed in other sphagesaurians such as Notosuchus terrestris and Mariliasuchus amarali. Body mass, estimated based on cranial length, displays a comparable pattern to that observed in body size with regard to these variations. However, the potential influence of factors such as the palaeoenvironment cannot be discounted.